Manufacture of lead oxides



April 14, 1931. c, J. wRlGHT MANUFACTURE 0F LEAD ox IDES Filed Sept, 17, 1925 Patented Apr. 1.4, 1943.1

UNITED STATES PATENT OFFICE CARL J'. WRIGHT, OF WEST NEW BRIGHTON, NEW YORK, ASSIGNOR TO COMBUSTION UTILITIES CORPORATION, OF NEW YORK, N. Y., A CORPORATION F MAINE MANUFACTURE OF LEAD OXIDES Application filed September The present invention relates to the manufacture of lead oxides and more particularly to the manufacture of red lead pigment.

According to the present invention, molten lead is agitated in contact with a current of heated air with the formation of lead monoxide. In case the inal product is to be red lead the-monoxide of lead formed as just stated, is then further agitated in contact with a current of heated gas derived at least in part from the same current as that involved in forming the monoxide to convert the monoxide into red lead pigment.

It is one of the objects of the present invention to provide a method of forming lead oxides which shall be rapid and also require a small amount of labor.

A further object of the present invention is to provide an apparatus suitable for carrying out the process just mentioned.

It is known that lead monoxide forms from molten lead at a temperature of about 7000 F. Itis known, moreover, that in the manufacture of red lead from lead monoxide the oxides should not be heated above 840 F. or thereabouts. Moreover, a certain amount of heat is formed in the reaction forming lead monoxide from metallic lead and also in the reaction forming red lead from' lead monoxide. The process and apparatus according to the present invention are designed to operate consistently with the facts as just stated.

Further objects and advantages of the process and apparatus according to the present invention will be apparent to those skilled in the art from the following description taken in connection with the accompanying drawing, in which Fig. 1 is an elevation of an apparatus according to the present invention and adapted to carry out the process according to the present invention, parts being shown in section and parts being broken away for purposes of illustration;

Fig. 2 is a partial section taken on the line 2-2 of Fig. 1.

In the apparatus according to the present invention, and illustrated in the drawing, the metallic lead is melted by hot gases which 17, 1925. Serial No. 56,988.

have first been used in forming lead oxides. Pot 10 is a receptacle in which the lead is melted as just mentioned, the body of pot 10 being held as illustrated within a chamber 12 in such position that the pot is in contact substantially over its entire surface with hot gases within the chamber 12 coming from the upper end of the rotary kiln 14. From the chamber 12, kiln gases pass to the atmosphere through a conduit 16.

The molten lead from chamber 10, however, passes downwardly through pipe 18 into the upper end of a second inclined rotary kiln 20, kiln 20 being on a lower level than kiln 14, and the pipe 18 running throughout its length through a current of hot gases contained in kilns 14 and 2O and chamber 2?, the chamber 23 just mentioned serving to connect the upper end of kiln 20 with the lower end of kiln 14. Heated air at a temperature of about 800 F. is injected into the lower end of kiln 20 through a pipe or nozzle 22 and the stream of heated air thereupon passes upwardly through the inclined kilns 20 and 14 into melting chamber 12. Within kiln 20, the molten lead dropping from the lower end of pipe 18 travels downwardly through this kiln countercurrent to the upwardly flowing stream of air. Within the kiln 20, moreover, the molten lead and the lead monoxide formed therefrom are continously agitated in contact with the air stream by being lifted and dropped repeatedly in their passage through the kiln. For the purpose of lifting and dropping the metallic lead and lead monoxide in contact with the air current as just mentioned, the interior surface of the kiln 2O is provided with a series of cells or pockets 24 covering substantially the entire inner surface of the kiln 20 and formed by two sets of intersecting ribs 26, 26 and 28, 28, projecting from the inner surface of the kiln 20, ribs 26, 26 being spaced and ,parallel and running longitudinally of the kiln while ribs 28, 28 are spaced and parallel and run circumferentially of the kiln 20.

The rate of travel of the metallic lead and lead monoxide downwardly through kiln 20 is determined, the inclination of the kiln having been fixed upon, by the speed of rotation of the kiln. According to the present invention, the R. P. M. 0f 'iln 20 is regulated with respect to the amount of heated air passing upwardly through the kiln so that some metallic lead is notconverted into monoxide within the kiln 20, but the monoxide formed together with metallic lead falls from the lower end of kiln 2() into separating pot 30. The molten metallic lead separates from the lead monoxide and settles to the bottom of the'pot 30, being drawn 0H therefrom through a pipe 32 whereas the lighter lead monoxide is drawn olf from pot 30 Aat a higher level than the melted lead through a downwardly inclined chute 34. The chute 34 delivers lead monoxide yto a bucket conveyer 36 by which the monoxide is elevated to a bin 3S. F rom the bin 38 the lead monoxide is delivered preferably by gravity into theupper end of kiln 14 by pipe 40 being illustrated in Fig. 1 as connecting the bin 38 with kiln 14 for this purpose. Within kiln14 the lead monoxide is lifted and dropped gin contact with an ascending current of hot air by means of a second set of cells or pockets 24h similar to those described in. connection with kiln 20. The lead monoxide is graduallyconverted into red lead as it passes through the kiln 14 and the` red lead drops from the lower end of this kiln into a chute 42 from which it is conv veyed away.

It will be obvious that lead monoxide from the pot 30 can be used as such instead of being converted into red lead. *When the lead monoxide is to be so converted, however, it is important that the temperature in kiln 20 shouldnot be permitted to rise tothe point at which any of the, lead monoxide is injured forthe purpose of forming red lead. vCertain othery uses of lead monoxide also require that the temperature be regulated and kept down during the course .of the manufacture of the lead monoxide. For the purpose of prevent-- ing an undesirable rise in temperature in the upper part of kiln 20, a stream of relativelyV cold air is introduced into the kiln 2O through pipe 44 the point of delivery of pipe 44 vbeing preferably slightly above the mid-point of the kiln 20. The air delivered through `pipe 44 not only supplies fresh oxide to the gas stream to compensate for that absorbed in the production of lead monoxide in the lower end of kiln 20, but also absorbs by its lower temperature the excess heat produced the formation Vof lead monoxide. from lead within kiln 20. v

The gas streamfromthe upper end if kiln 2O passes into the lower endA of kiln 14.

through the chamber 23 and in order to pra4 vent the temperature of the gases in kiln 14 from rising to the point at which red lead formation Vis interferedwith, it is preferred to introduce into the chamber 23 an additional supply of relatively 'cold air through 'the pipe 46. Pipes 44 and46 are provided with valves 45 and 47 respectively as illustrated whereby the amount of cooling air delivered through these pipes may be regulated to produce the desired results in kilns 14 and 20.

lHeated air from the nozzle 22 tobe injected into the lower end of kiln 20 may be supplied conveniently by forcing air through a coil of pipe 48 contained in a stack V50. Stack 50 may be conveniently yarranged, above `a chamber 31 surrounding thelower end of kiln 2() and in which the pot 30 is placed. Heating gases for'producing the desired temperature of the coil48 may be introduced into the ystack 50 through a passage 52 leading from-'the furnace 54-in which is a gas burner 56 or other'convenientheating means.

Moreover chambers 12 and 23 protect both ends of kiln 14 and the rupperV end ofkiln 20 from lossof heat by radiation. It is an important featureaccording to lthepresent invention that the temperature :gradients within the kilns 14 and 20 have no 'abrupt changes adjacent the ends lof the kilns as would inevitably occur if the ends of the kilns were not inclosed by chambers adapted to prevent loss of heat energy by radiation.V

lt is desired also that'the'lower end of kiln 2O be protected from the introduction of cold air. not coming from nozzle 22 and for this purpose, the joint between kiln 2O and the wall of chamber 31 at. the point 5.8 is so constructed as to admit a minimum of air.

Chamber 31,*also prevents the loss of'heatl from the lower end of kiln 2O by means of radiation as well as acting as holder for the pot 30. Y

The joints atthe pointsA 60, 62 and 64 be-.v

ard'construction and are illustrated as mount;V j.

edy on rotating trunnions 66, 66. VThe kilns 14 and 20, moreover, maybe rotated by'any convenient means, worm drives being illustrated for this purpose as indicated at (i8, 68. 1t will be understood that the motors, electric or otherwise, for driving the worm 68 are lia? preferablyof variable speed design whereby the speed ofkilns 14 and 20 may be readily adj usted or regulated if necessary, toproperly (ro-relate the speed of movement of theV solids longitudinally thereof vto the speed of movement-of the gas current therethrough.

lt will be understood that chambers 12,

'23 and 31 are formedof materials adapted to prevent loss of kheat by conduction through vthe walls thereof and l have illustratedat G7 a special insulating lining for Ythe chamber 23. Similar'linings may be used with the chambers 12 and l134 if 'df-isired.

Moreover,n the kilns 14 and 20 are inaderof'non-lieat co`n'' ducting materials or provided with non-heat conducting or heat insulating layers (not illustrated) to prevent loss of heat through the walls of the kilns and to maintain a uniform temperature gradient within the kilns during operation.

As above described, the lead for making oxides according to the present invention is melted in the pot 10 and preferably by means of waste heat in the outgoing cases. Vhenever desirable, however, an auxiliary burner may be installed in chamber l2 beneath the pot l() to assist in melting or to raise the temperature of the lead in pot lO.

Having thus described my invention, I claim:

l. The method of making lead oxide com prising intimately contacting a stream of molten lead in subdivided form with a moving stream of substantially pure air preheated to a temperature of about 800O F.

2. The method of making lead oxide comprising intimately contacting a downwardly flowing stream of molten lead with a counter currently flowing stream of hot substantially pure air, and regulating the rates of flow of said lead and air streams so that a portion of the lead remains unoxidized at the time of its removal from contact with said air stream.

3. The method of making lead oxide comprising repeatedly lifting and dropping molten lead transversely of the path of a diagonally upwardly flowing stream of air while moving said lead and oxide diagonally downward countercurrently to the flow of said preheated substantially pure air stream.

4. The method of making red lead comprising moving molten lead with agitation countercurrent to a stream of air, separating lead oxide from said stream and reintroducing said oxide into said stream and forming red lead from said oxide in said stream.

5. The method of making red lead comprising intimately contacting molten lead with a stream of hot air to form lead monoxide, introducing relatively cool air into said stream, and forming red lead from said monoxide in said stream after the introduction of said cooler air.

6. The method of making red lea-d coniprising intimately contacting molten lead With a countercurrent stream of air, separating lead oxide from said stream, introducing cooler air into said stream, reintroducing said monoxide into said stream and forming red lead from said monoxide in said stream at a point subsequent to the introduction of said cooler air.

7. An apparatus for forming red lead comprising a conduit, means for moving molten lead through a portion of said conduit in a given direction, means for passing a stream of air through said portion of the conduit in a direction opposite to that of said lead, means for agitating said lead in contact with said air, means for separating lead oxide from said molten lead, means for reintroducing said oxide into said conduit in the second portion thereof, and means for agitating said lead oxide in contact with said stream of air in the second portion of the said conduit.

8. The method of making lead oxide comprising introducing molten lead into the upper end of an inclined rotary kiln, introducing hot air into the lower end of said kiln, lifting and dropping said lead in said current of hot air, and so regulating the travel of the lead and oxide in the kiln with respect to the flow and temperature of said air that a portion of the lead remains unoxidized upon issuing from the lower end of the kiln.

9. The method of making red lead comprising moving melted lead with agitation countercurrent to a stream of hot air, regulating the flow of said lead with respect to the flow and temperature of said air so that a portion of the lead remains unoxidized upon removal from said stream, separating oxide from said unoxidized lead, re-introducing said lead oxide into said stream, and forming red lead from said oxide in said stream.

10. The method of making red lead comprising moving molten lead with agitation countercurrent to a stream of hot air, regulating the flow of said lea-d with respect to said air so that a certain portion of said lead remains unoxidized after its passage through said stream, separating lead monoxide formed in said stream from said unoxidized lead, introducing relatively cooler air into said stream, reintroducing said monoxide into said stream, and forming red lead from said monoxide in said stream at a point intermediate the re-introduction of said monoxide and point of introducing said cooler air.

l1. Apparatus for making red lead comprising an inclined rotary kiln, means for introducing hot air into the l-ower end of said kiln, a second inclined rotary kiln, means for conducting hot gases from the upper end of said first kiln into the lower end of said second kiln, and a lead pot set in the current of hot gases issuing from said second kiln.

12. An apparatus for making lead oxide comprising an inclined rotary kiln, means for introducing hot air into the lower end of said kiln, a lead pot arranged to be heated by the gases after leaving said kiln, a pipe for conducting molten lead connecting said pot with the upper end of said kiln, and means whereby a curr-ent of hot gases from said kiln is maintained around said pipe.

13. An apparatus for making lead oxide comprising a pair of inclined rotary kilns set at diderent levels and inclined oppositely one to the other, means for introducing molten lead through the upper end of the lower of said kilns, means for introducing hot air into the lower end of the lower of said kilns, means at the lower end of said lower kiln for separating metallic lead' from lead oxide,l means for introducing` said oxidey into the.x upper end of said upper kilmand chambersl surrounding the ends of said kilns, oneo sai-di `chambers servingito conduct gases fromsthe lower to the upper ofsaid kilns: and: all? of. said chambers acting to prevent. radiation from the ends of saidY kilns;

111. An apparatus for' forming. lead oxidel comprising a rotary kilnvinclinedv to thehorizontalsealed against the leakageV of air thereinto, an air preheater, a.` pipe 'or introducing! hot air-tromfsaidpreheater into the lowerend of said kiln, a meltingpot and connectionsg for introducing moltenf lead into the upper end of said kiln, pockets on the-interior ot"l said kiln arranged for lift-ing and dropping said molten lead ink itspassage through said kiln, and a'Val-'vedfpipe for introducing cooler air int-o saidk-iln intermediate the'points ofv introducing said-hot air andsaidlead.

15. The method of making lead oxidecomprising intimatelyv contacting countercurrently llowing streams of molten lead and preheated substantially pure' air in a kiln, the temperature of which` ismaintained at about 700Q F.

16. The methody of forming red' lead comprisin'g intimately contacting countercurrently flowing streams of molten lead and a' preheatedoxidizing gas streamat an elevated temperatureto produce lead monoxide, and intimately contacting lead monoxidey thus formed with said preheated'V oxidizing gasv stream at a still highertemperature' tov produ'cered lead. l

17. The method of forming'redlead comprising maintaining a temperature ofabout 700O Fl in a kiln while intimately contacting countercurrently flowing streams of molten' lead and preheated1 air therein, `and maintaining a temperature of about 840o F. in aY second kiln while intimately contacting lead monoxide formed in said lirst kiln with said countercurrently flowing stream of preheatedy oxidizing gas. Y y l 18. The method of converting lead int'o red' lead comprising intimately contacting molten lead with a iiowing stream of substantially pure air preheatedto a temperature of about 500O F., in a kiln maintained at a temperature of about' .700o Vll., and converting the leadmonoxide thus formed into red lead by intimately contacting it with a stream ofl preheated air in a second kiln maintained at a temperature oi'about' 840" F.

19. The method of making red lead comprising intimately contacting'` a, downwardly flowing stream oi molten lead with a countercurrent upwardlyr flowing stream of preheated air in a closed kiln,.so regulating the ratesaof travelof lead andair throughthekilnthat a mixture of unoxidizedleadand lead monoxide isremoVe'df-rom the lower end of the kiln,`

raciones separating the'lead from ther lead monoxidey through ai kiln in-directheat--transferringconLA tact with a countercurrently lowing stream of preheated air, passing: lead.A vmonoxide' forme-d in saidkiln c-ountercurrently through? another kiln in direct heat-transferringfcon- 'tactl with said. air' stream, and utilizing the` waste heat in said' air stream to. reduce said leadt'o a molten' stateipriorto introducing'it into said first named kiln. 1

In testimonyv whereot,1 aline` signature. 

